1. Field of the Invention
The present invention relates to a method of manufacturing a display that has a transparent protective plate on a surface of a display panel, and more particularly, to a display manufacturing method in which a transparent organic medium layer is formed between the protective plate and the display panel.
2. Description of the Related Art
Many of displays for home-use televisions and personal computers and information displays installed in public facilities are liquid crystal displays or organic electroluminescence displays. Liquid crystal displays are employed in a particularly wide range of products from as small ones as 2-inch monitors for cellular phones and the like to 60-inch or larger television monitors.
Most liquid crystal displays have two 0.2 to 0.7 mm-thick glass plates between which a liquid crystal is held. Some cellular phones, digital cameras, small-sized information terminals, and other devices where the liquid crystal panel surface is frequently touched during use therefore have a transparent protective plate in front of the liquid crystal panel to prevent external mechanical forces from disturbing displayed data or breaking the liquid crystal panel.
In personal computer monitors, home-use televisions, and other similar appliances, too, where the liquid crystal panel surface is touched less frequently, the liquid crystal panel itself could be shattered if something like tableware or a toy hits the liquid crystal panel surface with a large enough force.
Similarly to cellular phones, digital cameras, small-sized information terminals, and the like, some of such products as personal computer monitors and home-use televisions have a transparent protective plate 2 in front of a liquid crystal panel 1 as illustrated in FIG. 2 in order to prevent damage to the liquid crystal panel.
However, putting a transparent protective plate in front of a liquid crystal panel causes reflection of light at the interface between materials having different optical characteristics, specifically, refractive indices. In the case of the structure illustrated in FIG. 2, light is reflected at the interface between the protective plate 2 and the air existing in front of the protective plate 2, the interface between the protective plate 2 and an air layer 8 located behind the protective plate 2, and the interface between a first polarization plate 4 and the air layer 8. At these interfaces, it is observed that the difference in refractive index between materials causes the reflection of light, which significantly impairs the visibility of a displayed image especially in a bright environment.
In order to avoid this reflection of light due to a difference in refractive index, JP 05-11239 A and JP 2007-41534 A propose a panel structure in which a transparent interlayer 3 is formed instead of the air layer 8 between the protective plate 2 and the polarization plate 4 from an organic medium whose refractive index is the same as, or close to, that of the protective plate 2 and the polarization plate 4, thereby reducing reflection of external light and improving the visibility of a displayed image. (See FIGS. 3 and 4.)
The transparent interlayer 3 placed between the polarization plate 4, which is attached to a surface of the display panel 1, and the protective plate 2 is liquid or solid at room temperature in JP 05-11239 A and JP 2007-41534 A.
In the case where the transparent interlayer 3 is a liquid resin layer, the liquid transparent interlayer 3 whose refractive index is the same as, or close to, that of the polarization plate 4 and the protective plate 2 is sealed with a sealant 9 between the polarization plate 4, which is attached to the surface of the display panel 1, and the protective plate 2 as illustrated in FIG. 4.
In the case where the transparent interlayer 3 is solid, thermally curable resin or photo-curable resin is employed as a liquid organic medium, the liquid thermally curable, or photo-curable, resin is sealed with the sealant 9 between the polarization plate 4, which is attached to the surface of the display panel 1, and the protective plate 2 as described above, and then the resin is cured by heat or irradiation of light. Alternatively, a resin having the above-mentioned characteristics is shaped into a sheet having a desired thickness, and cured to obtain a sheet-shaped organic medium. The sheet-shaped organic medium is boned between the polarization plate 4, which is attached to the surface of the display panel 1, and the protective plate 2. A desired liquid crystal display 10 is thus manufactured.
Many laminated glass manufacturing methods similar to the ones described above have been proposed. A few of the proposed method of manufacturing laminated glass are introduced below.
1) Laminated Glass Manufacturing Method: Vacuum Bonding
The laminated glass manufacturing method that is employed most is the following vacuum bonding. This is a method of manufacturing laminated glass by, as described in the paragraph 0003 of JP 2005-187237 A, sandwiching an interlayer for laminated glass between at least two glass plates and deaerating the assembly with the use of a nip roll (pressure roll) (squeezing deaeration), or putting the assembly in a rubber bag to be suctioned under reduced pressure for preliminary press-fit, in which the air remaining between the glass plates and the interlayer for laminated glass is deaerated, and then heating and pressurizing the assembly in an autoclave for main press-fit.
The most common interlayer employed for such uses is polyvinyl butyral (PVB) plasticized by a plasticizer, because of its combined characteristics such as excellent adhesion with glass plates and synthetic resin plates, high tensile strength, and high transparency.
An interlayer used in this method sometimes has an embossed (concavo-convex) pattern on its surface in order that the spaces between the interlayer and the glass plates sandwiching the interlayer are deaerated better during bonding. In this case, the polymerization degree of a resin is lowered or the plasticizer content is increased in order to erase the embossed pattern more completely.
A problem of using a thermoplastic resin interlayer made of the PVB resin in this manufacturing method is that the interlayer needs to be bonded at high temperature and high pressure in an autoclave after temporary thermal bonding, which is laborious. Other problems include costly plant and equipment investment due to the installation of an autoclave, and poor production efficiency since the main press-fit using an autoclave is a batch process.
2) Laminated Glass Manufacturing Method: Atmospheric Bonding
JP 2001-31451 A and JP 2005-187237 A, for example, disclose methods capable of laminating glass at room temperature without needing temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave. These methods accomplish improved adhesion between the glass plates and the interlayer without temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave, by adjusting the physical properties and the like of the interlayer bonded between two glass plates in order to eliminate the necessity of performing temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave.
A manufacturing process using this interlayer is as follows:
First, a mold releasing film is peeled from one side of the interlayer, and one of two glass plates or synthetic resin plates is inserted between a nip roll and a rubber drive roll in such a manner that the interlayer is brought into contact with the glass (or synthetic resin) plate for the first time between the rolls, thereby sticking the interlayer to a surface of the glass (or synthetic resin) plate.
Next, the remaining mold releasing film is peeled, the glass (or synthetic resin) plate to which the interlayer has been stuck is placed to face the other glass (or synthetic resin) plate without contacting the other plate via the interlayer, and the ends of the two plates are nipped between the nip roll and the rubber drive roll in such a manner that the two plates are brought into contact with each other for the first time between the rolls, thereby bonding the two plates together in a continuous manner.
3) Laminated Glass Manufacturing Method: Liquid Resin Injection
As a different type of laminated glass manufacturing method that does not need temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave, JP 2005-89195 A and JP 07-290647 A disclose a method in which a liquid resin is injected into a space between glass plates and then cured at room temperature.
In this laminated glass manufacturing method, laminated glass having a space for injecting a liquid interlayer between two glass substrates is manufactured first, then a liquid interlayer resin is injected into the space between the two glass substrates, and the inlet is sealed after the injection is completed. Laminated glass having a liquid interlayer is obtained by this manufacturing method.
When a thermally curable resin or a photo-curable resin is employed for the liquid interlayer, laminated glass having a solid interlayer can be manufactured by heating the interlayer or irradiating the interlayer with light after injecting the liquid interlayer resin in the space between the two glass substrates and sealing the inlet.
JP 07-209635 A discloses a manufacturing method of a structure for preventing scattering of light in a liquid crystal display. This document's method using close bonding in a reduced-pressure atmosphere includes a first close bonding step in which a shock absorbing layer is closely bonded to a protective panel and a second close bonding step in which a liquid crystal cell is added to this assembly by close bonding. In the first close bonding step, the protective panel is placed on a substrate, and a liquid raw material capable of preventing scattering of light is poured from above the protective panel and cured. Alternatively, in the first close bonding step, a light scattering preventing material that is already cured and in a solid state is wound into a roll and put at an end of the protective panel, which is placed on a substrate. The roll is gradually unwound so that the solid light scattering preventing material is stuck to the protective panel while expelling air from under the roll. In the second close bonding step, the protective panel to which the shock absorbing layer has been closely bonded in the first close bonding step is put in a pressure reduction chamber. The protective panel is gradually lowered to be closely bonded to the liquid cell, while a suction pump connected to the pressure reduction chamber is driven to put the interior of the pressure reduction chamber in a reduced pressure atmosphere. This step does not necessarily need to be performed in a pressure reduction chamber if there is no trouble in expelling air from between the protective panel and the liquid crystal cell.
As mentioned above, several laminated glass manufacturing methods have been proposed as a way to bond a transparent interlayer between two hard display panels or between a hard display panel and a protective plate. However, the method of bonding a sheet-shaped transparent interlayer in vacuum has a problem in that the need to use an autoclave for a high-temperature, high-pressure process in order to obtain sufficient adhesion without trapping air bubbles makes the work laborious. Other problems of this method include costly plant and equipment investment due to the installation of an autoclave and poor production efficiency since the main press-fit using an autoclave is a batch process.
Although methods capable of laminating glass at room temperature without needing temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave have been published in order to solve the above-mentioned problems of vacuum bonding, these methods do not require temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave by adjusting the physical properties and the like of the interlayer bonded between two glass plates, and are therefore limited in terms of materials that can be employed in order to eliminate the necessity of performing temporary thermal bonding and a high-temperature, high-pressure process that uses an autoclave.
Other types of method have been proposed including one in which laminated glass having a space for injecting a liquid interlayer between two glass substrates is manufactured first, then a liquid interlayer resin is injected into the space between two glass substrates, the inlet is sealed after the injection is completed, and the interlayer is cured if necessary. This method, however, involves an injection length of the interlayer resin and has a fear of trapping air bubbles.